Method and system for tracking magnetic media with embedded optical servo tracks

ABSTRACT

A method and system for tracking storage media is provided that includes directing light through a first major side of a magnetic recording tape, wherein the tape includes optically detectable indicia embedded within the tape during formation of the indicia. At least a portion of the light may be detected after passing through the first side of the tape, and a change in the position of the tape based on the detected light may be determined.

BACKGROUND OF THE INVENTION

1.Field of the Invention

The invention relates generally to methods and systems for trackingmovement of storage media, and more specifically to methods and systemsfor tracking storage media with embedded optical tracking features tosense linear and lateral motion of the media.

2. Description of the Related Art

Digital tape-recording remains a viable solution for the storage oflarge amounts of data. Conventionally, at least two approaches areemployed for recording digital information onto magnetic recording tape.One approach calls for moving a magnetic tape past a rotating headstructure that reads and writes user information from discontinuoustransverse tracks. Interactive servo systems are typically employed tosynchronize rotation of the head structure with travel of the tape.Another approach is to draw the tape across, a non-rotating head at aconsiderable linear velocity. This approach is sometimes referred to aslinear “streaming” tape recording and playback.

Increased data storage capacity and retrieval performance is desired ofall commercially viable mass storage devices and media In the case oflinear tape recording, a popular trend is toward multi head,multichannel fixed head structures with narrowed recording gaps and datatrack widths so that many linear data tracks may be achieved on a tapemedium of a predetermined width, such as one-half inch width tape. Toincrease the storage density for a given cartridge size, the bits on thetape may be written to smaller areas and on a plurality of parallellongitudinal tracks. As more tracks are recorded on the tape, each trackbecomes increasingly narrow. As the tracks become more narrow, the tapebecomes,more susceptible to errors caused from the tape shifting up ordown (often referred to as lateral tape motion or “LTM”) in a directionperpendicular to the tape travel path as the tape passes by the magnetichead. In order to maintain proper alignment of the head with the datatracks on the tape, the tape is generally mechanically constrained tominimize lateral tape motion and data retrieval errors.

Lateral tape motion is generally defined as the peak-to-peak distance ofthe undesirable movement (in-plane) of the tape perpendicular to itsprescribed longitudinal direction of motion past a read/write head.Lateral tape motion and the ability to compensate for lateral tapemotion is a major limiting factor in determining the minimum width of atrack and the minimum spacing between tracks on the tape. Thus, aslateral tape motion is reduced, more tracks may be stored on the tapeand the tape density increases accordingly.

Tape substrates are also being made thinner to increase data storage fora given cartridge size. The thinner tape allows more tape to becontained within the same size diameter reel packages, therebyincreasing the data storage of the cartridge. Thinner tapes, however,are generally less rigid making them more susceptible to lateral tapemotion errors.

One approach to minimize lateral tape motion tracking errors is toprovide a multi-roller tape guide structure, such as the type describedin commonly assigned U.S. Pat. No. 5,414,585, entitled “Rotating TapeEdge Guide,” the disclosure thereof being incorporated herein byreference in its entirety. Such an approach has provided a viable “openloop” solution to lateral tape motion, i.e., control of lateral tapemotion without the use of feedback. The advent of new head technologies,such as magneto-resistive read heads, and new higher coercivityrecording media, data track widths have become very small, and manyadditional data tracks may be defined on the tape. Unfortunately,lateral tape motion remains as a limiting factor, and at certain datatrack width dimensions and data track densities, it is not possible tofollow the tape accurately enough to provide reliable performance duringreading and writing operations.

Several “closed loop” solutions have been developed to maintainalignment of a read/write head with data tracks and to minimize lateraltape motion tracking errors, including the use of magnetic servo trackspositioned on a the tape. Servo tracks allow for increased trackingabilities through servo track feedback mechanisms and the like. Thesemethods, however, have not been able to keep pace with the increaseddata capacity desired for magnetic tape storage media, includingincreasingly narrow data tracks and thinner storage media. A need existstherefore for an increased ability to track storage media, includinglateral tape motion, and allow for increased data storage capabilities.

BRIEF SUMMARY OF THE INVENTION

In one example of one aspect of the invention, a method for trackingstorage media is provided that includes directing light through a firstmajor side of a magnetic recording tape, wherein the tape includesoptically detectable indicia embedded within the tape during formationof the indicia, detecting at least a portion of the light after passingthrough the first side of the tape, and determining a change in theposition of the tape based on the detected light.

According to other examples of other aspects of the invention, methodsand systems are described for tracking storage media with opticallydetectable indicia embedded within the tape during formation of theindicia that include projection a light through one surface of thestorage medium to the optical detectable indicia. A detector may detectthe light that has passed through the surface of the storage medium andproduce a signal associated with the detected light. A magneticrecording head may then be moved in response to the signal.

The present invention is better understood upon consideration of thedetailed description below in conjunction with the accompanying drawingsand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a cross-sectional view and a plan view of anexemplary storage medium;

FIG. 2 illustrates a cross-sectional view of an exemplary storagemedium;

FIG. 3 illustrates a cross-sectional view of an exemplary storagemedium;

FIG. 4 illustrates an exemplary pattern of optically detectable indiciaembedded within a storage medium;

FIGS. 5A, 5B, and 5C illustrate various exemplary rad/write headstructures including an optical head for tracking storage media withembedded optical tracking features;

FIG. 6 illustrates an exemplary method for tracking storage media; and

FIG. 7 illustrates an exemplary pattern and method of tracking storagemedia.

DETAILED DESCRIPTION OF THE INVENTION

According to one aspect, a method is provided for optically trackingstorage media that include a plurality of embedded optically detectableindicia The following description is presented to enable any personskilled in the art to make and use the invention. Descriptions ofspecific materials, techniques, and applications are provided only asexamples. Various modifications to the examples described herein will bereadily apparent to those skilled in the art, and the general principlesdefined herein may be applied to other examples and applications withoutdeparting from the spirit and scope of the invention. Thus, the presentinvention is not intended to be limited to the examples described andshown, but is to be accorded the widest scope consistent with theprinciples and features disclosed.

As discussed above, although mechanical or open loop mechanisms areknown to reduce lateral tape motion to some degree, at certain highlinear track speeds and narrow track widths it is not practical to relyentirely upon open loop tape mechanisms. One solution for preventingerrors arising from lateral tape motion with closed loop feedback is setforth in U.S. patent application Ser. No. 09/046,723, entitled“Multi-Channel Magnetic Tape System Having Optical Tracking Servo,”which is incorporated by reference herein in-its entirety. As disclosedtherein, an optical servomechanism can be employed to track and monitorlateral motion of a magnetic tape relative to a recording head. To thisend, the magnetic tape may be provided with an optically detectableservo track that is etched onto a surface of the tape. The opticallydetectable servo track may include one or more narrow servo tracks alongthe length of the back surface of the tape, i.e., the surface oppositethe recording surface, that are optically detectable to provide finepositioning information for aligning a recording head with a magneticdata track.

Other exemplary optical servo track configurations include a series ofoptically detectable indicia or marks that are spaced apart by a uniformdistance along the length of a magnetic tape. For example, one'suchexample is described in U.S. patent application Ser. No. 09/718,818entitled, Systems and Method for Forming a Servo Pattern on a MagneticTape,” which is incorporated herein by reference in its entirety. Asdescribed therein, one method of forming servo tracks on a magnetic tapeincludes using a laser for ablating a surface of the magnetic tape.Laser ablation generally heats and burns a small hole or pit in a carbonlayer disposed on one surface of the tape. The process, however,generally causes a burst or small explosion that may result in thecreation of smoke or debris. The smoke or debris from the hole mayinterfere with the manufacturing process and the performance of themagnetic tape. For example, debris from forming the pits in the carbonlayer may clog or foul the magnetic tape as it is spooled onto a take-upreel. Further, the pits may not be formed of a uniform size or shape dueto the nature of laser ablation, i.e., burning the pits into the carbonlayer with bursts of heat Material left on the surface may alsointerfere with the optical detection of the pits by creating noise orfalse detections of servo tracks. Typically, the tape is thereforecleaned to remove debris and material after the pits are formed.Additionally, a protective coating is generally included over theindicia after they have been formed to protect them from damage such asscratches and the like during subsequent manufacturing steps or duringuse.

As data-tracks become-increasingly narrow and densely configured to meethigher storage demands, additional tracking systems and methods aredesired for magnetic storage media For example, increased trackingsensitivity to lateral tape motion and the like are desired to allow aread/write head to track increasingly narrow data tracks. Thus, oneexemplary storage medium described herein is provided wherein aplurality of optically detectable indicia are embedded within a magnetictape. An exemplary method for forming the plurality of indicia within anembedded layer of the magnetic tape is also described that may reduce oreliminate the creation of debris and create more precisely formedindicia Further, an exemplary method is described for tracking storagemedia with embedded servo tracks that may include detecting or accessingthe indicia from either of the two major sides of the magnetic storagemedia, e.g., the same or opposite surface as a magnetic recording layer.

Forming optical indicia embedded within the storage medium offersseveral advantages over conventional backside etching. For example, thedebris field created by laser ablation or the like is generallyeliminated. Further, more precise indicia may be formed with embeddedindicia than with a backside etch because the heat generated to form theindicia may be localized to a greater degree within an embedded portionof the storage medium. Eliminating the debris field and preciselyforming the indicia may reduce noise when detecting the indicia with anoptical detector. Therefore, more accurate linear tape motion detectionand tracking may be achieved. The ability to track the storage mediummore accurately may allow for more data tracks and increased datastorage capacity of the medium.

Additionally, in some examples, the embedded optically detectableindicia and patterned servo tracks are accessible from either side of astorage medium. For example, an optical head or the like may detect theindicia from either side of a magnetic tape. Accessing servo tracks fromboth sides of a magnetic tape allows for greater design flexibility fordrive configurations and compatibility of storage media with variousdrive configurations.

Further, the embedded indicia are protected from damage such asscratches and the like without an additional step of forming aprotective layer over the indicia after they have been formed. Forexample, scratches may be caused by a roller included in drive system orthe like and lead to inaccurate tracking of the storage medium.

The following description describes numerous aspects and examples of thepresent invention in greater detail. Further, an exemplary storage mediadevice for recording and/or retrieving stored data is described,including exemplary methods and systems for tracking the opticallydetectable indicia embedded in the storage media.

I. Storage Media

FIGS. 1A and 1B illustrate an exemplary configuration of optical indiciaor servo marks 110 embedded in a storage medium, for example,.a magneticrecording tape 100. FIG. 1A illustrates a cross-sectional view ofvarious layers that may be included in magnetic tape 100. FIG. 1Billustrates a plan view of a major side of magnetic tape 100 includingan exemplary pattern of servo marks 110 illustrated in outline ascircles.

With particular reference to FIG. 1A, the cross-sectional view of tape100 will be described. Tape 100 includes a base film 102, optical servolayer 120, which includes servo marks 110, outer layer coat 104, innerlayer 106, base film 108, inner layer 112, and magnetic storage layer114. Servo marks 110 are formed in servo layer 120 and embedded withintape. 100. Servo marks 110 may be patterned such that an optical head orthe like may detect and track the tape 100. Specifically, an opticalhead may direct light to and detect light from servo marks 110. Thelight detected may determine the position and movement of tape 100 inthe lateral and linear dimensions. A system with an optical head andservo controller may also maintain alignment of a read/write head (SeeFIG. 5A) with tape 100, during lateral motion of the tape 100.

Servo layer 120 may be an organic material such as carbon or the likewherein optically detectable indicia, such as servo marks 110, may beformed by a laser or the like. In particular, servo marks 110 may beformed by heating servo layer 120 with a laser such that localizedportions of servo layer 120 are heated and melt or deform to createregions of different reflectivity and/or phase than the surroundingservo layer 120. For example, servo marks 110 may be formed byultra-violet laser engraving or heating of servo layer 120 embeddedwithin magnetic tape 100. The heating may form pits or marks in theservo layer that are several microns or less in diameter. In otherexamples, ultraviolet or green wavelength lasers may be used to formservo marks 110. It should be recognized that servo marks 110 may beformed by any suitable method that localizes heat or energy to createindicia with different reflectivity and/or phase than the surroundingoptical layer 120. Further, servo layer 120 may be any material whereinservo marks 110 may be formed embedded within tape 100.

The formation of servo marks 110 does not create unwanted debris becauseservo marks 110 are not formed or burned while exposed to an exterior oftape 100. Further, heat used in forming servo marks 110 may be localizedwithin a smaller area of servo layer 120 than with conventional laserablation. The localized heat may allow servo marks 110 to be formedwithin servo layer 120 with increased precision. Further, embeddingservo layer 120 and servo marks 110 below the surface of tape 100, forexample, between base film 102 and recording layer 114, protects servomarks 110 from damage such as scratches and the like during manufactureand recording or play operations.

Additionally, servo marks 110 may be formed across the lateral width ofservo layer 120 and accessed or detected by an optical detector fromeither side of tape 100. For example, a laser may access servo marks 110from either major side of tape 100, i.e., through base film 102 orthrough the recording layer 114. In conventional backside etching of acarbon layer, the pits may be detected from only one side because thepits are generally not formed on both sides of the carbon layer. Accessto servo marks 110 from both sides of tape 100 allows a greater degreeof freedom in tracking and designing read/write heads to track tape 100.

In this example, servo layer 120 is disposed between base film 102 andouter layer coat 104. Base film 102 may include any suitable tapesubstrate, such as a flexible plastic substrate such as PolyEthyleneTerephthalate (PET), Polytthylene Naphthalene (PEN), PolyAramid (PA), orthe like. Typically, base film 102 provides tape 100 with a rigid basefor the magnetic storage layer 114 and the servo layer 120. Further, itis desired that base film 102 be at least partially transmissive to thewavelength of the particular laser or other means used to form servomarks 110 in servo layer 120 if servo marks 110 are formed through theside of tape 100 that base film 102 is located. For example, if a laseror the like passes through base film 102 when forming servo marks 110,it is desirable that the base film 102 not be altered in a manner thataffects the performance of tape 100. Further, base film 102 should betransmissive to the light used to detect and track servo marks 110 if itis desired to detect servo marks 110 through the same side of tape 100.

Tape 100 may further include outer layer coat 104, inner layer 106, basefilm 108, inner layer 112, and magnetic storage layer 114. Outer layercoat 104 is provided on the side of servo layer 120 opposite the basefilm 102. Outer layer coat 104 may include a flexible plastic materialor the like. Tape 100 may further include an inner layer 106 formedadjacent the outer layer coat 104 and a second base film 108 disposedadjacent the inner layer 104. An inner layer 112 and magnetic storagelayer 114 are disposed adjacent the second base film 108. Any of outerlayer coat 104, inner layer 106, base film 108, and inner layer 112 mayinclude any suitable tape material, such as a transparent polymermaterial or the like, as is known in the art for magnetic tapes. Themagnetic storage layer 114 may include gamma ferric oxide, chromiumdioxide, Metal Powder (MP) or any other suitable material(s) formagnetically recording and storing information.

The various layers of tape 100 may be bound together with an adhesive,such as an organic resin or the like. Further, some layers may bedeposited or formed over adjacent layers. It should further berecognized that various other materials and layers may be includedwithin tape 100 depending on the particular application. It should alsobe recognized that various layers described herein may be omitted fromtape 100 as is known by those skilled in the art.

Tape 100 preferably has a lateral tape width of approximately 0.500inches, however any lateral width tape 100 is contemplated. Further, thethickness of tape 100 may be approximately 0.005 inches, althoughthinner or thicker tapes are contemplated.

With reference to FIG. 1B, an exemplary pattern of servo marks 110embedded within tape 100 is described in greater detail. Servo marks 110may be positioned at substantially uniform intervals in the lineardimension and substantially uniform intervals in the lateral dimensionof tape 100. Typically, the spacing between servo marks 110 in thelinear dimension depends on the desired sampling frequency of theposition of the tape, and the spacing in the lateral dimension, dependson the desired resolution of detection and servo control of the lateraltape motion. For example, the spacing in the linear dimension may bebetween about 2 and 200 microns, and the spacing in the lateraldimension may be between about 2 and 100 microns. Preferably, thespacing is between about 2 and 100 microns in the linear dimension andbetween about 2 and 20 microns in the lateral dimension, and morepreferably about 100 microns in the linear dimension and 10 microns inthe lateral dimension; however, greater or smaller spacings arecontemplated. As will be described in greater detail, however, numerouspatterns may be employed depending on the particular application andthese spacings should not be viewed as limiting the possible patterns ofservo marks 110.

Servo marks 110 may extend the full length of magnetic tape 100 in thelinear dimension to form servo tracks that may be followed by an opticalservo controller. In this instance, three servo tracks are shown whereeach servo track is defined by a linear row of marks 110. An opticalhead may track the servo tracks as tape 100 is streamed or otherwisemoved relative to the optical head. Measurements by the optical head maybe used as feedback to align a read/write head with one or more datatracks recorded on the magnetic tape 100. In some examples, multiplerows of marks 110 may form a single servo track to be followed by anoptical head.

The distance from the center-to-center of servo marks 110 in the lineardimension is defined herein as distance C. In one example, thetransverse size or diameter of servo marks 110 is defined by distance d.The spacing between adjacent servo marks 110, i.e., the distance betweenthe closest edges of two adjacent servo marks 110, is defined bydistance A. Servo marks 110 are spaced apart from center-to-center inthe lateral dimension by distance c, and from adjacent servo marks 110by distance a The various distances may be varied depending on theparticular application. Further, in some examples, servo marks 110 maybe offset in the lateral dimension as described below (see FIG. 7).

The distance c between marks 110 in the lateral dimension of the tape100 determines, at least in part, the resolution of the optical servohead, i.e., how precisely the optical head can detect and control motionin the lateral direction of tape 100. The spacing may be based on acharacteristic of the tape, i.e., the lateral resolution desired toaccurately track data tracks with a read/write head. Further, thedistance between marks 110 in the linear dimension of the tapedetermines how often the servo head samples or measures the lateralposition of tape 100.

The spatial distance C between servo marks 110 may be varied dependingon the system and method for tracking servo marks 110. For instance, agiven sampling frequency depends in part upon the linear speed of thetape 100 and spacing between servo marks 110 when data is read orretrieved by a read/write system. More generally, the pattern, e.g,number and spacing, of servo marks 110 in the lateral and lineardimension depends on the particular application and system. For example,the number and spacing of servo marks 110 may be varied depending on thedesired sampling frequency, resolution, linear speed of tape 100, andthe like.

It should be recognized, however, that any pattern of embedded servomarks 110 are possible. For example, servo tracks may be formed ofcontinuous lines, as well as patterned and/or non-identical shapes, suchas squares, triangles, saw tooth shapes, and the like. Further, theexact distances between servo marks 110 in either the linear or lateraldimension may vary depending on the accuracy of the method used to formservo marks 110 and the desired application. Other exemplary patterns ofoptically detectable servo marks and servo tracks are described in abovereferenced U.S. patent application Ser. Nos. 09/046,723 and 09/718,818both of which are incorporated herein by reference in their entirety.

Further, only three servo tracks of marks 110 are shown in FIG. 1B,however, it will be understood that any number of servo tracks may beincluded along the full length of the tape 100 to provide an opticalservo track that can be monitored and tracked by the optical servosystem. Additionally, it will be understood that servo marks 110 may beaccessible from the same side of tape 100 as recorded magnetic datatracks or on the opposite side thereof.

With reference to FIG. 2, a cross-sectional view of tape 200 isillustrated. As illustrated, tape 200 may include multiple layers. Inthis instance, tape 200 includes a base film 202, a magnetic storagelayer 214, servo pattern layer 220, inner layer 212, and back coat layer221. Base film 202 may include a plastic substrate or the like toprovide a rigid base for the magnetic storage layer 214 and servopattern layer 220. On one side of base film 202 magnetic storage layer214 may be disposed. Magnetic storage layer 214 may include a pluralityof data tracks. An inner layer 212 may further be formed between baselayer 202 and storage layer 214.

A servo pattern layer 220 may be located adjacent base film 202 on aside of base film 202 opposite of storage layer 214. Servo layer 220includes a pattern of servo marks 110, for example, as illustrated inFIG. 1B. Servo layer 110 may include carbon or other suitable materialfor forming servo marks 110 therein. A protective layer 221 may beprovided adjacent servo layer 220. Protective layer 221 may be, forexample, a thin transparent layer or the like that is desirablytransmissive to a laser or other method used for forming servo marks110. It should be recognized that protective layer 22i, as well as otherlayers disposed between servo layer 220 and an optical head, need not betransparent to visible light; rather, the layers should be transparentto the optical frequency used to detect servo marks 110. For example, ifan optical head uses an infrared or ultraviolet laser to detect servomarks 110, protective layer 221 should be at least transparent toinfrared or ultraviolet light to allow the optical head access to servomarks 110.

FIG. 3 illustrates a cross-sectional view of another exemplary tape 300.Tape 300 includes base layer 302, servo layer 320, inner-layer 312, andstorage layer 314. In this example, servo layer 320 is disposed betweenbase layer 302 and inner layer 312. In certain applications, inner layer312 may be omitted such that servo layer 320 is disposed between baselayer 302 and storage layer 314.

With regard to FIGS. 2 and 3, it should be recognized by those skilledin the art that various additional layers may be included with exemplarytapes 200 and 300. Certain layers may also be omitted, such as innerlayer 212. Further, magnetic storage layers 214 and 314 maybe formed onand accessible from both major sides of tapes 200 and 300, i.e., bothsides of the lateral width, depending on the particular application.

FIG. 4 illustrates an exemplary pattern of embedded optical servo tracksin magnetic tape 400. In this instance, magnetic tape 400 includes aplurality of densely spaced servo tracks that are grouped into aplurality of bands 420. Bands 420 are positioned laterally across thewidth of the tape 400 and may extend linearly for the length of the tape400. Tape 400 includes four bands 420 where each band includes seventeenservo tracks to provide sixty-eight servo tracks in all for tape 400.The tracks in the linear direction may include servo marks 410 in theform of holes, circles, or other optically detectable indicia embeddedin tape 400 that extend along the length of the tape 400 or band 420. Inone-example, servo marks 400 are configured with approximately equalspacing in the lateral dimension and approximately equal spacing in thelinear dimension. For example, a desired resolution of the optical headto measure and correct for lateral motion may dictate the dimension ofthe lateral and/or linear spacing.

Each band 420 of servo marks 410 may correspond to a band or group ofdata tracks on tape 400. A band or group of data tracks is oftenreferred to as a data zone on the magnetic tape 400. For example, a bandof data tracks may be included on tape 400 adjacent a band 420 of servomarks 410. Alternatively, data tracks may be interlaced with bands 420when viewed from a major side of tape 400.

In one example, fourteen of the tracks may be employed as servo tracks412 that correspond to data tracks of the magnetic recording layer (notshown) of tape 400. Two auxiliary servo tracks 414 may be located nearthe lower portion of the band 420 and one auxiliary servo track 416located near the upper portion of the band 420. The auxiliary servotracks 414 and 416 may include control information as well as delimitthe edges of the band 420. The exact number of servo tracks employed maybe altered depending on the particular application and desired accuracyof detecting lateral motion of tape 400. Generally, increasing thenumber of servo tracks 412 increases the detection accuracy of anoptical head or the like.

It should be recognized that the exemplary configuration of servo marks410 and servo tracks 412, 414, and 416 are illustrative only. Variousother methods and schemes may be employed for configuring servo trackson magnetic storage media as are known in the art.

II. Exemplary Method of Tracking Embedded Optical Servo Tracks

FIG. 5A illustrates one embodiment of a magnetic read/write headstructure 512 including an optical servo head 534 for tracking opticallydetectable indicia embedded within an exemplary recording medium.Generally, FIG. 5A depicts a head carrage assembly for a magnetic taperecording and retrieving system capable of being translated laterallyrelative to a tape path. The tape system may include a fine positioningsystem and a coarse positioning system for maintaining magnetic headstructure 512 adjacent to the tape path. The tape system may furtherinclude various other components known in the art such as reels, tapeguides, servo control electronics and motors, microprocessor/controller,and the like. For the sake of clarity, however, various other componentsthat may be included have been omitted.

In the instant example, a read/write head structure 512 and magneticrecording tape 500 are illustrated. Magnetic recording tape 500 is shownbeing drawn through read/write head structure 512 between arms 562 and564. The tape may be drawn between a supply reel and a take-up reelalong a nominal linear tape path through read/write head structure 512.The tape 500 is moved with a relative linear velocity, for example,approximately 120 inches per second. Because of the relatively highlinear velocity and contact between tape 500 and various mechanical tapeguides, head elements, and the like, movement of the tape 500 along thenominal tape path may result in undesirable additional tape movements,in particular, lateral tape motion.

As discussed previously; although various mechanical or open loopmechanisms are known to reduce lateral tape motion to some degree, atcertain high linear track speeds and narrow track widths it is notpractical to rely entirely upon open loop tape mechanisms. Accordingly,magnetic recording tape 500 may include an optical servo trackingpattern embedded in a servo layer 520 of tape 500 to provide a moreprecise closed loop servo tracking mechanism. For each data track ofmagnetic recording layer 514 there may be an associated optical servotracking pattern, such that if the optical servo head 534 follows theappropriate servo track pattern during linear tape movement, themagnetic head array 536 may follow the data tracks despite lateral tapemotion.

In particular, read/write head 512 includes a first arm 562, a secondarm 564, a magnetic head array 536, an optical servo head 534, analignment signal output 545, and a cross-arm 566. FIG. 5A depicts therelationship between the magnetic head array 536, shown as a read/writesubstrate, the optical servo head 534 and the tape 500. Specifically,tape 500 sits in a gap formed between the first arm 562 and second arm564. Arm 564 includes the optical servo head 534 and disposes theoptical servo head 534 adjacent one side of the tape 500. Similarly, arm562 carries the magnetic head array 536 and disposes the substrate 536adjacent to the recording side of the tape 500. The cross-arm 566 holdsthe arms 564 and 562 in a known, typically fixed relationship such thatthe relative alignment of the optical servo head 534 and the magnetichead array 536 is known. Accordingly, the head structure 512 depicted inFIG. 5A maintains a data transfer mechanism, such as magnetic head array536, in a known spatial relationship with the optical servo head 534,thereby allowing for alignment of the data transfer mechanism responsiveto a determination of the alignment of the optical servo head relativeto the recording medium.

Magnetic head array 536 may include multiple read and write headelements aligned to read some, but not all of the magnetic data storagetracks 506. The write elements are preferably realized as thin filmmagnetic write structures, and the read elements may be thin film ormagneto-resistive read elements. Magnetic head array 536 may include,for example, eight or 16 magneto-resistive read transducers. With theparticular arrangement of heads shown in FIG. 5A, the effectiverecording area tape 500 may be divided into multiple zones or bands ofparallel magnetic recording tracks as well as multiple bands of servotracks shown as 521 a and 521 b embedded within a servo layer 520. Thearrangement may-therefore include a head positioner-mechanism thatcoarsely positions the head structure 512 and magnetic head array 536within a particular zone of the tape 500, for example, corresponding toband 521 a. Additionally, to follow the tape despite lateral tapemotion, the head positioner mechanism includes optical servo head 534that may detect the embedded servo track pattern and provide feedbackcontrol of the head structure 512.

Optical head 534 may operate to emit and receive light to detect opticalservo marks embedded in tape 500. Optical head 534 may include a laserlight source that emits a beam, or beam pattern, that can be employedfor tracking one or more servo tracks. The laser may be, for example, anultraviolet laser, infrared laser, or the like capable of detectingembedded indicia. In particular, the light emitted from optical head 534may pass through tape 500 to reflect or diffract from the embedded marksformed in the servo layer 520. The light may pass through either majorside of tape 500, i.e., the magnetic recording layer 514 side or thebase film 515 side of tape 500.

An exemplary semiconductor device that includes a laser light sourcethat may be used with an optical head according to one example isdescribed in U.S. Pat. No. 5,729,519, the disclosure of which isincorporated herein by reference.: It is believed that the semiconductordevice described in the above referenced U.S. Patent is embodied in theHUL7001 device manufactured and sold by the Matsushita Company ofTakatsuki Japan. Other suitable devices, for example, sold by MatsushitaCompany include the HUL7202 and other HUL72XX devices. The device actsto emit and receive a pattern of light that may be focused onto theservo layer of tape 500 to provide a selected pattern of spots. Thepattern of spots provided by the optical head 534 may correspond to acharacteristic of the optically detectable servo tracks carried on theservo layer of tape 500. For example, the optical head 534 may provide abeam configuration that can be focused onto the servo layer of tape 500to provide a pattern of spots that corresponds to spatialcharacteristics of the optically detectable servo tracks, such as byproviding a pattern of spots that will overlay completely, or selectedportions of a pattern of servo marks embedded within tape 500. It shouldbe recognized, however, that any suitable light emitting device may beused.

In alternative examples, the optical head 534 may include other elementsand devices for carrying out the emission and reception of light. Thesemay include emission and reception devices that comprise an assembly ofdiscrete optical elements, as well as other semiconductor devices, orhybrid devices. In further alternative examples, the optical servo head534 may include separate devices for emitting and receiving light, aswell as separate devices for emitting and receiving each of the separatebeams. Separate emission and reception devices may also be located oncommon or opposite sides of tape 500. Moreover, the optical servo headsmay include light emission and reception devices that include filters,anti-glare coatings, multiple light sources, integrated focusingelements, and the like. Accordingly, it will be understood by one ofordinary skill in the art that the exemplary optical servo head 534 mayemploy any suitable device for emitting and receiving light fordetecting an optical servo track, and the optical servo head 534 is notto be limited to any particular device or system configuration.

Further, optical servo head 534 may act as a transducer that provides acontrol signal, typically an error signal. To this end the emission andreception system of the depicted embodiment can be coupled directly intoan electrical circuit. Specifically, FIG. 5A illustrates that theoptical head 534 includes a servo control signal 545 that may be coupledto an electronic circuit or the like, such as an electronic servo-loopcircuit that processes signals generated by the optical servo head 534to align the head structure 512 with data tracks on the magnetic tape500.

A tape drive system may further include a computer processor forprocessing the servo control signal 545 provided by the optical servohead 534 to determine various characteristics of the moving tape, suchas the direction of the tape, the speed of the tape, the longitudinalposition of the tape, and the like. For example, the system may includeany suitable microprocessor/microcontroller system that may beprogrammed for processing the information collected by the optical servohead 10. The computer processor may process signals from optical head534 to provide coarse and fine head positions based upon servo loopcontrols and the like. The fine head position control loop may respondto tape position information sensed by the optical head 534 based on oneof the servo track patterns that corresponds to the set or group oflinear tracks presently being followed. Any positional offset orposition error sensed by the optical head 534 may result in a correctivedriving current signal to move the head accordingly for correctalignment with the magnetic data record tape tracks being followed asthe optical head 534 follows a particular servo track pattern.

FIG. 5B illustrates another exemplary magnetic read/write head structure582 including an optical servo head 534 for tracking opticallydetectable indicia embedded within an exemplary recording medium. Tape500 may stream by optical head 534 and read/write head 536 along alinear tape path. Magnetic read/write head structure 582 may be similarto magnetic read/write head structure 512 except that the optical head534 is located on arm 562 with read/write head 536 and arm 564 may beomitted. With the optical head 534 and read/write head 536 positioned onthe same side of tape 500 the light from the optical head 534 passesthrough magnetic layer 514 to detect servo layer 521 a (see FIG. 5A). Inparticular, light that is incident, at least in part, upon the servomarks may be reflected back to a higher degree (or in some instances toa lower degree) to, the optical head 534 than light that is not incidentupon embedded servo marks. Light that is not incident upon servo markswill have a higher transmission rate through tape 500 and lessreflection detected by optical head 534. It should be noted that ingeneral a portion of the light will be reflected and transmitted througheach layer of tape 500.

FIG. 5C illustrates another exemplary magnetic read/write head structure592 including an optical servo head 534 for tracking opticallydetectable indicia embedded within an exemplary recording mediumMagnetic read/write head structure 582 may be similar to magneticread/write head structure 512 except that a light source 534 a islocated on one arm, e.g., arm 562, and the detector 534 b is located onan opposite arm, e.g., arm 564. Magnetic read/write head structure 536and light source 534 a may be located on arm 562 similar to FIG. 5B,however, head structure 536 is omitted from FIG. 5C for illustrativepurposes to clearly show the relationship between light source 534 a anddetector 534 b. It should be recognized that light source 534 a anddetector 534 b may be interchanged on arms 562 and 564 depending on theparticular application and system design.

In this example, the various layers of tape 500, e.g., the base layer515, servo layer 520, recording layer 514 and the like may havedifferent transmission and reflectance properties to the optical beam.The servo marks 110 embedded in servo layer 520 may have a differenttransmission rate and/or reflectivity rate. For example, the materialselection of the servo layer may result in servo marks 110 scatteringincident light to a greater degree than the surrounding servo layer andreflecting less light. The optical detector 534 b may therefore bedisposed on an opposite side of tape 500 as the light source 534 a andconfigured to measure the light that passes through tape 500.Alternatively, optical detector 534 b may be disposed on the same sideof tape 500 as the light source 534 a and configured to measure thelight that passes through a portion of tape 500 and reflects backtowards the detector 534 b. Signal output 545 a from light source 534 aand signal output 545 b from optical detector 534 b may by used by acomputer processor or the like to provide coarse and fine head positionsbased upon servo loop controls as described with regard to FIG. 5A.

With reference to FIG. 6, an exemplary pattern of optical beams 670 isillustrated superimposed over a pattern of servo marks 610 embeddedwithin tape 600. In this example, three servo tracks are shown, however,it will be understood that any number of servo tracks may be used alongthe length of the tape 600 to provide an optical servo track patternthat may be monitored and tracked by an optical servo system. Further,any number of optical beams may be employed to track the position andmovement of tape 600.

As tape 600 moves linearly in the direction of linear motion indicatedin FIG. 6, optical servo marks 610 are carried linearly across the frontof optical head 534 (FIGS. 5A-5C). As servo marks 610 move by opticalhead 534, the optical head 534 may activate one or more light sources togenerate one or more optical beams directed to one side of tape 600. Thelight emitted by the light source may pass through various diffractiongrating, lenses, prisms, and the like to diffract the light into adiffraction pattern that includes, for example, a zero order beam and aplurality of higher order beams. In one example, the pattern emittedfrom the light source may be configured and focused by suitable opticalelements into a multi-beam configuration that includes a zero order beamand two first order beams, both of which first order beams travel alongan axis that is transverse to the axis along which the zero order beamtravels. The thee beams 670 may therefore be focused to pass through asurface of tape 600 to the servo layer of tape 600 in a pattern that issuited for detecting the pattern of marks 610 embedded within tape 600.

The optical beams 670 of the exemplary pattern illustrated in FIG. 6 areprojected to have a diameter approximately one-third the size of thediameter of servo marks 610. The diameter of servo marks 610 may be inthe range of 2 to 15 microns, for example, and the beams might beconfigured to have a diameter approximately one-third that size. In thisexample, for a properly aligned tape 600, both the upper and lower servomarks 600 will reflect an equal intensity (or phase) of light back to areceiver or detector such as a photodetector or the like. For a tapethat has moved laterally relative to an optical servo head, andtherefore is out of alignment, the diffraction pattern emitted from theoptical servo head will fail to align with the pattern of servo mark's670 on tape 600, and a detector or detectors will measure differentlevels of intensity. For example, if tape 600 moves laterally upwardrelative to an optical servo head, the upper servo mark 610 will moveupward, thereby being repositioned further into the upper beam 670 that,when properly aligned, impinges on only the upper half of servo mark610. Simultaneously, the lower servo mark 610 will also move upward,thereby being repositioned away from the lower beam 670 that, whenproperly aligned, impinges on the lower half of the servo mark 610.Accordingly, the upper servo mark 610 will reflect more light back tothe optical servo head and the lower servo mark 610 will reflect lesslight back to the optical servo head and one detector will measure acorresponding increase in reflected light intensity and one detectorwill measure a corresponding decrease in reflected light intensity. Thisprovides a push-pull tracking mode control signal that allows the systemto sense lateral movement of the tape 600 that is less than the diameterof a single servo mark 610. Accordingly, the systems described hereincan detect lateral movement of the tape that is less than one micron,i.e., sub-micron.

Continuing with the example of the push-pull tracking method and system,it is understood that an optical head may provide signals correspondingto the increasing and decreasing intensity levels that arise when thetape 600 moves laterally with respect to the optical head. As describedin the above mentioned U.S. patent application “Multi-Channel MagneticTape System Having Optical Tracking Servo,” these signals may beprovided to a differential servo control system that employs thedifference between these two signals to adjust the position of theoptical head (and the recording head) relative to the position of tape600. The servo control system may move the optical head and magneticrecording head to maintain proper alignment with tape 600.

FIG. 7 illustrates an exemplary method for tracking motion of a tape 700that includes servo marks 710 configured along an offset axis. Forexample, servo marks 710 of tape 700 are aligned along an axis that istilted at an angle of approximately θ relative to an axis extendingperpendicular to the direction of linear tape movement Preferably, theangle of offset is approximately 7 degrees, but other angles may beadvantageously used depending on the particular application. An offsetconfiguration of servo marks 710 provides a leading mark, and a laggingmark that may provide phase information and allow an optical servo headto detect the direction of travel of tape 700.

As discussed above, the optical servo head may project optical beams orspots onto portions of tape 700 to employ a push-pull tracking modedetection system and achieve fine control over the head/tape alignment.Additionally, it will be understood that the optical servo head can beemployed for providing tape speed information. Specifically, as thepitch between servo marks 710 on-the tape 700 may be a fixed knownvalue, and as the sets of servo marks 710 may extend along, the fulllength of tape 700, the detection information provided by an opticalhead may provide a measure of the rate at which the sets of servo marks710 are passing in front of the optical servo head. Accordingly, theoptical servo head may detect that marks 710 are passing in front of thetape at a given frequency, which for a known linear spacing betweenmarks 710, may be translated into an inch/second tape rate.

It should be recognized that lateral or linear tape motion of any ofthese examples may be determined with only the center mark, or any onema, without employing the push-pull method. Further, other servo trackdetection techniques can be employed without departing from the scope ofthe invention. Additionally, in other examples, the optical servo headcan be employed to read information on the tape, either encoded on aseparate track, or encoded within the servo track. For example, theoptical track can be employed to provide information representative ofthe longitudinal location of the section of the tape adjacent theread/write head. To this end, the tape can include encoded down-the-tapelocation information for indexing the longitudinal position of the tape.Additionally, the optical servo head can be employed for detectinginformation representative of the section of tape, or the band of tapebeing processed, for tapes that are subdivided into sections, such asbands of data. The optical servo head can also be employed for detectingcross-tape position information, or any other type of information thatmay be helpful to read or write data onto the storage media.

The above detailed description is provided to illustrate exemplaryembodiments and is not intended to be limiting. It will be apparent tothose skilled in the art that numerous modification and variationswithin the scope of the present invention are possible. For example,various servo patterns and detection methods are within thecontemplation of the invention. Further,.numerous other materials andprocesses not explicitly described herein may be used within the scopeof the exemplary methods and structures described as will be recognizedby those skilled in the art. Accordingly, the present invention isdefined by the appended claims and should not be limited by thedescription herein.

1. A method for tracking storage media, comprising: directing lightthrough a first major side of a magnetic recording tape, wherein thetape includes optically detectable indicia embedded within the tapeduring formation of the indicia; detecting at least a portion of thelight after passing through the first side of the tape; and determininga change in the position of the tape based on the detected light.
 2. Themethod of claim 1, wherein a change in the position of the tape isdetermined by measuring the intensity of the detected light.
 3. Themethod of claim 1, wherein a change in the position of the tape isdetermined by measuring a change in the phase of the detected light. 4.The method of claim 1, wherein a change in the position of the tape isdetermined by measuring a change in the transmission of the lightthrough the first side of the tape and an opposite second side of thetape.
 5. The method of claim 1, wherein a change in the position of thetape is determined by measuring a change in the reflection of the lightfrom the optical indicia.
 6. The method of claim 1, wherein light isdetected from a second major side of the tape opposite the first side ofthe tape.
 7. The method of claim 1, further including at least one ofreading or writing data to a magnetic recording layer from the firstside of the tape.
 8. The method of claim 1, wherein the light includesan ultra violet light source.
 9. The method of claim 1, wherein thelight includes an infrared light source.
 10. The method of claim 1,wherein the light produces a beam of light with a cross-sectional sizesmaller than a cross-sectional size of the indicia
 11. The method ofclaim 1, wherein the light includes two or more beams of light.
 12. Themethod of claim 11, wherein the two or more beams of light overlay atleast partially the indicia.
 13. The method of claim 11, wherein the twoor more beams of light are detected separately.
 14. The method of claim11, further including producing a control signal associated withdetection of the two or more beams of light, wherein the control signalindicates movement of the tape.
 15. The method of claim 1, furtherincluding producing a control signal associated with the change in theposition of the tape.
 16. The method of claim 15, wherein the controlsignal controls a servomechanism to adjust a magnetic recording head.17. The method of claim 1, wherein the indicia include a plurality ofmarks aligned with substantially equal spacing along a linear length ofthe tape.
 18. The method of claim 1, wherein the indicia include aplurality of marks aligned in tracks with substantially equal spacingalong a linear dimension of the tape and substantially equal spacingbetween the tracks in the lateral dimension of the tape.
 19. The methodof claim 18, wherein the indicia in the lateral dimension are off-setwith respect to each other
 20. The method of claim 18, wherein theindicia in the lateral dimension are off-set with respect to each byapproximately 7 degrees.
 21. A method for reading storage mediaincluding a magnetic data track and optically detectable indicia,comprising: moving a magnetic tape with optically detectable indiciaembedded within the tape during formation relative to a magneticrecording head; projecting light through a portion of said magnetic tapeto the indicia; detecting at least a portion of the light transmittedthrough a portion of the magnetic tape; producing a signal associatedwith the detected light; and moving the position of the magneticrecording head in response to the signal.
 22. The method of claim 21,wherein the projected light is reflected from the indicia to a greaterdegree than the surrounding tape.
 23. The method of claim 21, wherein achange in the position of the tape is determined by measuring a changein the transmission of the light through a first major side of the tapeand an opposite second major side of the tape.
 24. The method of claim21, wherein a change in the position of the tape is determined bymeasuring a change in the reflection of the light from the opticalindicia.
 25. The method of claim 21, wherein the phase of the projectedlight is changed by the indicia.
 26. The method of claim 21, furtherincluding measuring the intensity of the detected light transmittedthrough a portion of the magnetic tape.
 27. The method of claim 21,wherein the signal is used as feedback in a servo control system todetermine the direction to move the magnetic recording head.
 28. Themethod of claim 21, wherein the signal is used as feedback in a servocontrol system to determine the magnitude to move the magnetic recordinghead.
 29. The method of claim 21, wherein the light includes threeoptical beams that overlay selected portions of the indicia.
 30. Themethod of claim 29, further including detecting the intensity of thethree optical beams and operating a servo control system in a push-pulltracking mode.
 31. The method of claim 21, further including positioningthe magnetic head and an optical head on opposites sides of the tape,wherein the magnetic head and the optical head are in a fixedrelationship.
 32. The method of claim 21, further including positioningthe magnetic head and an optical head on the same side of the tape,wherein the magnetic head and the optical head are in a fixedrelationship.
 33. A system for at least one of reading and writing datato one or more tracks on a magnetic recording medium comprising: amagnetic recording medium including optically detectable indiciaembedded within the tape during formation of the indicia; a magneticdata head for at least reading or writing data to the recording medium;a light source positioned to project a pattern of light through saidrecording medium to the indicia; a detector capable of detecting thepattern of light generated from said laser light source; and a servocontroller, wherein the servo controller moves the magnetic data headbased on a change in the pattern of light detected by the detector. 34.The system of claim 33, wherein said recording medium includes amagnetic recording tape.
 35. The system of claim 33, wherein the lightsource includes a laser.
 36. The system of claim 33, wherein the lightsource includes an ultraviolet laser.
 37. The system of claim 33,wherein the light source includes an infrared laser.
 38. The system ofclaim 33, wherein the magnetic head and the detector are in a fixedrelationship with respect to each other.
 39. The system of claim 33,wherein the magnetic head and the detector are positioned on the sameside of the recording medium.
 40. The system of claim 33, wherein themagnetic head and the detector are positioned on opposite sides of therecording medium
 41. The system of claim 33, wherein the detectorproduces a signal associated with the detected light.
 42. The system ofclaim 41, wherein the signal is used as feedback in a servo controlsystem to determine the direction to move the magnetic recording head.43. The system of claim 33, wherein the detected light includes apattern of spots.
 44. The system of claim 43, wherein the detectorproduces a signal associated with the pattern of spots.
 45. The systemof claim 44, wherein the signal is used as feedback in a servo controlsystem to determine the direction to move the magnetic recording head.46. The system of claim 44, wherein the signal is used as feedback in aservo control system in a push-pull tracking mode.
 47. The system ofclaim 33, wherein the detector produces a signal as a function of theintensity of the light incident thereon.